- Todd See
North Carolina State University
Department of Animal Science
Raleigh, NC 27695-7621
The overall goals for sow productivity are a program that 1) maximizes number of pigs per litter; 2) optimizes pig birth weight; 3) maximizes litters per year; 4) maximizes lactation yield; and 5) optimizes longevity and lifetime productivity. In order to accomplish these goals it is important to understand the breeding cycle as diagramed in Figure 1. Sow productivity depends heavily on the management of the breeding female population. This paper will focus on five general management considerations to optimize sow productivity including genetics, nutrition, environment, management, stress and breeding.
Figure 1. Critical periods for successful breeding and gestation of sows
During the 1990’s, simultaneous advances were made in pigs/sow/year, predominantly due to management, and lean (growth rate and percentage), predominantly due to genetics. Today, we are managing a more prolific, leaner, and larger mature sow than during 70’s and 80’s. In addition, gilts now grow faster, reach puberty at a heavier weight, and are mated both younger and leaner.
Breeding females of lean genotypes must maintain condition throughout breeding life. This can be accomplished by minimizing lactation fat losses and encouraging gestation fat recovery. Several gilt studies have clearly demonstrated that backfat depths of less than 0.5 inches are associated with reproductive inefficiencies. However, reduced reproductive performance is also consistently reported in females having more than 1 to 1.2 inches of fat when they are introduced into the herd. There appears to be an optimal gilt body condition range for introduction to the breeding herd that is dependent on genetic line. With leaner genetics, there is a substantial increase in maintenance requirement throughout lactation; thus management actions to encourage feed intake are needed. The combination of heat stress with substantial loss of body stores in thin females demands better reproductive management than a situation involving females with higher appetites and increased fat deposits.
When considering different genetic lines, an important consideration is knowing which performance testing methods and selection objectives were used. It has been well documented that selection for efficient lean growth can adversely affect reproductive performance. Selection for reduced backfat will result in reduced daily feed intake, increased age at puberty, fewer pigs born alive, greater preweaning mortality, and more nonproductive days. Litter size at birth and weaning and piglet weaning weight are also reduced with selection for low daily feed intake. The consequences of today’s genetically leaner animal can result in reduced reproductive performance and, most importantly, reduced appetites.
Mechanized Buildings—The first step in reducing the impact of the environment on sow fertility is to make sure ventilation systems are in good working order and are providing adequate air movement. Minimum enclosed facility ventilation rates for a sow and litter, gestating sow, and breeding sow or boar during the summer months are 500, 180, and 300 CFMs/hd, respectively, however, these rates may be doubled during the summer months in the southeastern U.S.. Conduct a thorough maintenance inspection and test the ventilation system to ensure that these rates are met. It is not uncommon to find that (even in fairly new operations) ventilation systems do not operate as designed. Unless these systems are delivering the required ventilation rates, other management practices suggested here will not be effective. Additionally, fresh air must enter rooms at a speed of 600-1,000 ft/min. in order to circulate well and prevent cold air from falling on animals (drafts). Don’t overlook the fresh air inlets; adjustments should be made seasonally. A good, year-round air-inlet-speed-goal is 900 ft/min.
Some operations also have installed components in mechanically ventilated gestation and breeding facilities called cool cells. Cool cells can be effective in keeping room temperatures 10 to 15 degrees cooler than outside temperatures by pulling the fresh air through wetted corrugated material. Another effective method to cool sows during lactation is the installation of nose coolers. In farrowing rooms that use negative pressure systems with a plenum as the air inlet source, a tube can be connected to the plenum and directed to the bottom of the farrowing crate near the sow’s nose while she is lying down. This supplies constant air movement across her face when the ventilation system is activated.
The activation temperature for these systems should be set between 75° and 78° F. While this practice may not maintain a farrowing room temperature 75° to 78° when outdoor ambient temperature reaches 90° +, it will keep the room from heating up as quickly, because the cooling process will begin sooner. Pigs are more sensitive than humans to the combined effects of heat and relative humidity because they do not sweat. Thus, it is important to consider heat indexes and to adjust the activation temperatures of supplemental cooling systems. The simplest way to calculate the heat index to determine it by using the figure below or visiting the Weather Calculator on the Web site of the National Weather Service office in El Paso, Texas at: http://www.srh.noaa.gov/elp/wxcalc/heatindex.html
For example, if it is 75° F in the barn, but the heat index is over 85° due to high humidity, the supplemental cooling system needs to be active. It is imperative that supplemental cooling systems are in place in all phases of sow production. These could include evaporative drip or spray cooling and circulating fans. Sprinkling is preferred to fogging, which uses smaller water droplets. Sprinkling cools the skin surface by wetting the skin and allowing the water to evaporate, where fogging cools the air and then the air must cool the skin. Most systems are designed to operate for a period of 1 to 2 minutes, up to 4 times per hour. Spray nozzles should provide at least 0.02 gallons of water per hour per head. Low-pressure drip systems in the farrowing house should be rated for 0.5 to 1 gallon per hour. The use of sprinklers has been shown to increase feed intake and reduce body weight loss (Table 1; McGlone et al., 1988) during lactation.
Table 1. The effect of management on the appetite of lactating sows
|Water drip||Snout coolers||Feed intake
|Body weight change
(McGlone, Stansbury and Tribble, 1988)
Along with earlier activation of the cooling systems, replacing heat lamps with regular, “household,” 100-watt incandescent bulbs will reduce the ambient temperature of the farrowing room. Positioning heat lamps at the maximum distance away from the sows head will also reduce the impact of this supplemental piglet heat on the sow. Finally, heat lamps may need to be shut off or run on timers (off/day: on/night) during periods when temperatures do not fall below 85° F to help reduce room temperatures. If this strategy is practiced, a source of light will be needed somewhere in the room because some producers report lactation failure if sows and litters are subjected to total continuous darkness.
Periods of elevated temperatures also can harm the gilt pool. It is not uncommon to see increased periods of anestrus, shorter estrus periods, and lower conception rates in gilts during this time. In controlled studies, when higher temperatures were found to induce anestrus in gilts, cyclicity resumed after exposure for as little as 1 to 2 days to a relatively normal thermal environment. It may be possible to utilize this concept on commercial farms by constructing a “cool zone” in the breeding barn for the gilts. The minimum period that gilts will need to be exposed to this environment to resume cycling has not been determined, which means that if 2 to 3 weeks of gilts are required, a fairly large area in the breeding barn may be needed. Furthermore, cold water and air movement may not be sufficient cooling mechanisms when one considers humidity to be an equal contributor to heat stress. Consequently, some type of air conditioning system may be needed to remove humidity. The cost of this type of system may not be justified unless there are extensive problems with anestrus (< 10% cycling).
Naturally Ventilated Facilities—Some gestation and breeding facilities consist of a naturally ventilated, curtain sided or open sided building. For these facilities, minimum ventilation rates are not measured by air movement rates (CFM’s), but are arbitrarily evaluated based on animal comfort. Management of non-mechanically ventilated buildings is fairly easy if the buildings were constructed with adequate side air inlet openings and orientated (east/west) to accommodate natural airflow. During hot weather, ventilation rates must be high enough to prevent overheating. Increased airflow is achieved by maximizing ridge openings and air inlets on both sides of the building. Furthermore, since we generally tend to ventilate for human comfort which is usually 3-4 feet above the pig level, air deflecting panels to direct air currents downward into the pig zone may be necessary to provided satisfactory ventilation at the pig level. It is important to consider supplemental cooling methods like evaporative cooling and circulator fans in naturally ventilated buildings and they are applied as previously described in the mechanized building section.
For today’s lean genotype sow there is a substantially increased maintenance requirement and during lactation the pressure is on management actions to encourage feed intake. This can be accomplished in part by minimizing lactation fat losses and encouraging gestation fat recovery.
For sows post weaning the objective is for them to conceive in 3 to 5 days with as large a litter as possible. There is no advantage to “drying off” sows by restricting feed in this 3 to 4 day period. Instead restricting feed is more likely to delay heat. Sows should be feed to appetite postweaning (6 to 8 lb.) and for the first 3 weeks of pregnancy fed to achieve large litter size. Both high and low feeding levels for the first 3 weeks may compromise the number of fetuses. Feeding levels for this period will range from 4 to 6 lb. daily.
Sows and gilts should be provided enough feed following breeding to keep them on an even plane at maintenance levels or slightly above for thin females. The pre-mating nutritional status appears to be a greater determinant of embryo numbers and survival than post-mating ration in gilts. Using this strategy requires “flushing” them with an extra 1 to 2 pounds of feed during the estrus cycle before mating. This can be attempted for sows as well, though most postweaned sows voluntarily restrict their own feed intake. Keep in mind that high feed intake during the 30 days following breeding may have a negative impact on swine embryos, especially in pregnant gilts.
Management during gestation should provide for a planned increase of 80-100 lb. for parity 1, 80-90 lb. for parity 2-5, and 55 lb. for sows greater than fifth parity (Johnston, 1996) fat depth should also increase by about .2 in. (5 mm). These targets will vary according to sow maturity, body weight at conception and body condition. Overfeeding in gestation has a well proven negative impact on feed intake in lactation and results in fat and lean tissue loss to provide for milk production. Gestation feeding programs need to ensure the female is consuming around 4 to 5 pounds, depending on diet formulation, of feed daily.
Measurement of fat depth, condition scoring and weighing sows are all effective ways to feed the gestating sow to target weight and body condition at farrowing. Backfat measurement although relatively simple is not always convenient. In this case, sow condition scores are very good indicators of body fatness. Backfat or condition score combined with body weight gives an even greater level of accuracy in assessing the sow’s nutritional needs. Feeding to condition demands that when a sow is seen to be in lower condition than she need be, the feed allowance should be increased; if the sow is in higher condition feed allowance should be reduced. The condition score demands that the animal be fed what it requires, not a previously stipulated amount. Condition scores and their related backfat depths may also vary by the genotype that they are applied to. The problems associated with condition scoring systems are: 1) this is an indirect measure of fat depth and errors can be dependent on sow size and shape. 2) Condition score is dependent on the opinion of the scoring technician and standards can shift over time. 3) The response of condition score to change in feed intake is not well documented and is variable.
Under ad libitum conditions the daily feed intake of the lactating sow will be between 6.5 and 20 lb. daily. Lactation weight and fat losses are directly related to lactation feed intake. Higher feed intakes may achieve maternal body weight gain and fatty tissue balance. Lactation weight losses may be largely prevented at feed intakes above 11 lb. per day, which may be quite readily achieved. Lactation fat losses may be largely prevented at feed intakes above 18 lb. per day that are not at all readily achieved.
The following points help to ensure maximal appetite during lactation. Obviously diets should be balanced so that all nutrients are provided in the correct proportions for nutritional requirements and energy balance. Ingredients should also be selected that are easily digestible. Flavors of sweeteners may be added to provide a consistent taste.
Increase Feeding Frequency—When producers switch from feeding two times per day to three times per day, most experience a 10 to 15 percent increase in sow feed intake. There are some farms in North Carolina that actually feed four or more times per day in the summer. The main thing to remember is that when you increase the frequency of feeding, you must decrease the amount that you feed each time. For example, if you are feeding 6 pounds twice a day (12 pounds total), then when you increase to three times per day, you may want to feed around 6 pounds at the first feeding and 4 pounds at each subsequent feeding (14 pounds total).
The reason this strategy works is related to the normal increase in body temperature that occurs after a sow consumes a meal. Theoretically, there won’t be as big an increase in a sow’s body temperature after she eats 4.5 pounds (as after she eats 6 pounds) because there will be less feed to be digested. Consequently, this could be very important for sows whose body temperatures already may be in the upper end of the thermoneutral range due to high temperatures in their environment.
Keep Feed Fresh—Sows tend to be picky eaters compared to most animals. In warm conditions, feed is more likely to spoil, especially if it contains high levels of fat. Increasing the feeding frequency in conjunction with feeding slightly smaller meals is an excellent way to keep feed fresh.
Try Liquid Diets—Liquid feeding is a common practice to increase feed intake in many finishing operations and can be implemented during lactation. However, because of the short period of time that sows are actually in lactation, it may be more beneficial to acclimate females to this change of diet during late gestation. Success with this strategy may vary greatly among operations, but it has been reported to boost sow feed intake by as much as 15 percent. One drawback is that wet feed does not stay fresh in the trough for very long and molds will also accumulate without regular cleaning.
Add Fat to the Diet—As a result of poor feed intake, many sows are not able to meet the metabolic demands of lactation and may fall into a negative energy balance. This factor probably accounts for most of the reproductive disorders during periods of elevated temperatures. One way to ensure that sows are consuming enough energy, even though they are eating a smaller quantity of feed, is to add fat to the lactation diet. Supplemental fat (7 to 10 percent animal or vegetable fat) will increase the dietary metabolic energy content of the feed.
There are two important considerations in adopting this practice. First, a diet containing high amounts of fat will become rancid more rapidly than a traditional diet with only 1 to 2 percent fat. Sows will not eat rancid feed. Therefore, feeding smaller quantities more often and smelling feed leftover in the sow feeder at each feeding to check for spoilage should be a standard practice. Second, because sows are consuming less feed, dietary levels of essential vitamins and minerals also need to be boosted to compensate for less feed consumed on a daily basis.
Give Water Constantly—High ambient temperatures will increase water requirements. Increased water consumption coupled with increased urinary water loss is one mechanism by which pigs lose body heat. An increase in ambient temperature from 54°-60° F to 86°-95° F will cause pigs to drink more than 50 percent more water. Nursing sows need to consume 8 to 10.5 gallons of water every day, and gestating sows need 3 to 5 gallons. One rule-of-thumb to follow is a water-to-feed ratio of 5:1. Fresh, constant water is also critical during breeding and gestation. The watering system should deliver a minimum of 0.25 gallons per minute and ideally 0.5 gallons per minute. Sows will quickly become frustrated if the flow rate is low, and this will reduce their appetite for dry feed. Water temperature and quality are also important. During periods of high temperatures, pigs will consume almost double the quantity of cool water (50º F) as warm water (80º F).
Environment, social status, and stress have all been shown to interact with reproduction. In principle, any management strategies that can reduced stress and allow for some social interaction with other animals will enhance the well being of animals and consequently, reproductive performance. Importantly, stress prior to, during, and following breeding can result in higher incidences of embryo mortality. One of the most common mistakes in management is a failure to recognize that during breeding and gestation, females are also susceptible to heat stress when temperatures reach and exceed 80 -85°F for short or extended periods of time (Flowers, 1997). Heat stress has its most detrimental effect on reproductive performance during two critical stages of the gestation period, the first 30 days and the last 30 days. Consider that in the normal breeding female, 30% of the potential litter number (number of eggs ovulated) are lost within the first 30 days of pregnancy making management of the female in the first 30 days critical to the producing large litters of viable pigs.
Prenatal mortality may be as high as 40 percent in pigs. The majority of this embryo loss occurs during the first two to three weeks following breeding. Factors associated with embryo loss include stage of pregnancy, disease, age of dam, genetic factors, nutrition, external environment, intrauterine environment, and stress-including heat stress. The following recommendations can be put into effect to avoid increased embryo mortality:
- avoid late estrual inseminations,
- minimize unnecessary stress by mixing females only at weaning,
- refrain from or even stop moving females in gestation to different locations, and
- don’t raise or lower feeding levels within the first 30 days after breeding with expectations of improving reproductive performance. Provide a good, level plane of nutrition during and after breeding. The strategies also should be used through the year.
Late Insemination—Several processes occur following breeding to optimally prepare the uterus for implantation. A postbreeding inflammatory response occurs in the uterus of the pig to remove nonfertilizing spermatozoa and bacteria. In addition, during early to mid-estrus, uterine contractions help physically to remove the products of this inflammation. The first step in limiting embryo loss occurs during the estrus period, and that is to avoid late inseminations. The simplest way to prevent late estrual inseminations is to ignore the “target” number of inseminations and breed females totally on the basis of a strong, standing heat response. Another way to reduce mistimed inseminations is to determine the average estrous length in your weaned sows, gilts, and repeat breeders and based on these averages, shorten the last insemination interval. For example, if you normally service sows AM day 1, AM day 2, AM day 3, change your schedule to AM day 1, AM/PM day 2. Thorough heat-checking before performing subsequent inseminations will help prevent poorly timed, late artificial inseminations, which may interfere with uterine preparation for implantation.
Mixing Females—Once fertilization occurs in the oviducts, pig embryos descend into the uterus 24-48 hr after ovulation. However, implantation does not occur until day 13 and full attachment not until day 28. During this time, the pig is highly susceptible to stress factors, such as movement and temperature. If females are to be mixed, this should be performed on the day of weaning to prevent unnecessary stress on the female. Any unnecessary stress following breeding can result in embryo detachment and loss.
Moving Females—After breeding and around day 30 of pregnancy, females may be moved to a different location; however, mixing sows and gilts at any time during or following breeding greatly increases the chances of subsequent embryo mortality. Temperature changes also are likely to increase embryo mortality, and during early pregnancy females should be protected from heat or cold in order to avoid unnecessary stress. Make sure that cooling and heating systems are routinely maintained and functional. You should have a backup system in place (i.e., hoses and spray nozzles) in case of equipment failures.
Another way of closing the gap between lactation feed intake and needs is by reducing the sow’s nutritional requirements. Possibilities include a shorter lactation period, cross fostering to balance litter size for suckling and split weaning. Summarized records from Mabry and Culberston (1998) showed that parity 3+ sows can be weaned, recycle and conceive efficiently at lactation lengths as short as 9 days. However, first and second parity sows appear to need lactation lengths of 14 and 12-d cycle, respectfully, to cycle and conceive efficiently.
Reducing litter size during the last 1/3 of lactation by means of “split weaning” can also be an effective strategy for conserving body fat stores of the sow. However, some studies suggest the removal of more than 2-3 piglets earlier than 3 days prior to weaning may cause sows to cycle while still in the farrowing crate. Short cycling can be avoided and split weaning accomplished by removal of the heaviest 2 or 3 piglets three days in advance of weaning
Research has shown that reproductive performance of females and boars on farms where the animals have little fear of humans is higher than on farms where animals were fearful of humans, so proper handling of animals can impact herd performance. In all cases, however, producers must be aware of the hazards associated with handling large female and male animals throughout the production cycle, particularly when animals are exhibiting sexual aggression.
Facility, pen and alley design all influence the ease with which a producer can move and handle the animals in the breeding herd. Alleyways should be wide enough to allow passage of single animals in the breeding area (24 to 30 inches wide). An ample supply of gates that will swing from either end, having dependable latches and in locations which allow precise direction of animal traffic is essential. Breeding pens and AI collection areas should have designated “safe areas” for workers to escape to if a boar or female becomes aggressive while mating. In some cases, vertical pipes located across a corner of a breeding pen and spaced wide enough for only the person to squeeze between (8-10 inches) are utilized.
Recent findings have shown that routine vaccinations and injections given to breeding animals should not be given by the personnel who routinely handle the animals and should, instead, be given by personnel outside the production area whenever possible. This practice helps with the subsequent handling ability of the animals due to a reduction in fear toward the person giving the injection.
Insemination—Technicians need an adequate knowledge of physiology and anatomy in order to make prudent decisions while inseminating females. It is not surprising that differences exist between technicians and reproductive performance (Table 2).
Table 2. Effect of AI technician (256 sow / technician)
|Technician||Farrowing Rate (%)||# Born Alive / Litter||Total # Born / Litter||# Pigs Produced|
Another concern is what is referred to as insemination fatigue. It appears that farrowing rates may decline when individuals are presented a large number of females in estrus at a given time (Table 3). Strategies should be in place to detect and correct this potential problem. The development of a standard routine with rest breaks after 10 to 15 sows is suggested.
Table 3. Inseminator fatigue
|Matings / Day||Technician (n)||Farrowing Rate (%)||Born Alive|
With exclusive AI, commingling the sow and boar can be frustrating because of inability to move the female away from the boar to perform an AI. Therefore, bringing the sow and boar in close proximity, allowing fence-line nose to nose contact and applying backpressure to the female should provide sufficient stimulation to detect estrus. For sows housed in crates, running a boar in front of sows while a breeding technician applies backpressure is a common and effective method of estrus detection. When the boar is directly in front of a female in a crate, she will move forward and assume the standing reflex. It is imperative in this situation that the boar be in direct nose-to-nose contact with the female because often non-estrual females in crates will “act” like they are in heat until the boar contacts them.
Heat detection – Increasing the frequency of estrus detection will provide for a more accurate determination of the true beginning and end of estrus. Estrus detection is a very labour intense and time-consuming procedure, and consequently, most operations do not check heat more than once per day. However, it may be cost-effective to heat check sows twice a day for 3 to 4 breeding periods in order to accurately establish an average estrus length relative to return-to-estrus intervals. This assessment will enable the farm to develop an efficient insemination protocol for either once or twice per day estrus detection schedules. If an operation chooses to switch back to only morning heat checks, the timing of the first insemination can be adjusted based on the expected length of estrus for that group of females. In most cases, a shorter interval between estrus detection and first insemination will be required when heat detection is performed once vs. twice per day since these female may have been in estrous for a longer period of time prior to detection.
The period from the beginning of one heat to the beginning of the next heat is called the estrus cycle. The physiological and behavioral aspects of estrus are caused by increasing estrogen. Females will first go through a period known as proestrus. This is the time when they show signs of approaching estrus. It can be from one to four days in length. During this time, the female seems more excited and increasingly aware of her environment. The vulva of the gilt becomes more swollen and red in color than it does in a sow. The gilt has a much longer and more pronounced proestrus than a sow.
Physiological signs are the swelling of the vulva and clitoris, and a mucous discharge. Behavioral signs are increased activity, increased vocalizations, mounting activity and standing reflex. Before a sow or gilt is mated, check for as many signs of heat as can be determined by the following:
- Swollen red vulva. This will be more prominent in gilts and actually starts to dissipate at the end of proestrus.
- Evidence of a sticky, viscous secretion at the vulva. The “stickiness” can be measured by a procedure known as “thumb checking”. This is done by touching the thumb to the vulva in order to get a smear of the secretion on the thumb. Press the index finger and thumb together and pull apart to “measure” the stickiness. The stickier the mucous, the stronger the heat.
- Groaning of sow. When a sow is in heat sometimes she will emit a deep groaning sound. This usually occurs at a peak of the etrous cycle.
- Tendency of a female to stand upon application of back pressure. Her ears will prick erect and the sow or gilt will tend to “lock” up. Sometimes if heat is suspected, the person checking heat must briskly rub the sow’s side low in the flank with one hand while pushing down on her loin just rear of center. The belly rubbing stimulates the “nosing” of the boar.
- When in doubt, take the sow or gilt to the boar. Most of the time, the two together will let you know if the female is in heat.
Remember that each female is an individual and will show slightly different signs of estrous. Systematic and consistent heat checks enable one to become familiar with the normal situation of all females and when it changes to estrous. The standing reflex is enhanced by intense periods of boar exposure. However, prolonged boar exposure may result in habituation and fatigue. Boars should be used to check for estrus in small groups. If the boar is placed in the alley in front of the sow then estrus detection is a two person job; one handles the boar and the other checks the sow.
Semen Storage—Fertility of semen extended in the most widely used extenders, even under ideal conditions, decreases during storage (Figure 2). The rate of this decline is dependent upon such factors as individual boars and extender used. Semen collection and delivery systems should be developed that insure a high percentage of females are inseminated with semen stored for less than 2 or 3 days. Avoid, as much as possible, utilizing semen that has been in storage for more than 48 hours.
Most extenders are designed for semen storage at 17-18°C. An on-farm semen storage unit should be utilized that will maintain a constant temperature. A high-low thermometer should be used to monitor storage conditions. Semen containers should be stored in a horizontal position and be gently rotated twice per day.
Figure 2. Effect of extender and storage time on farrowing rate (Laforest and Allard, 1996)
Timing of Insemination—Assuming high quality semen is provided, the key to a successful AI program is heat detection. Most studies indicate that sows ovulate about 40 hours after the beginning of standing heat. However, there is variation among sows in time of ovulation and the exact time of standing heat is usually unknown.
It has been demonstrated (Kemp et al., 1996) that sows which have a relatively short wean to first estrus interval tend to stand longer than sows which have a longer wean to first estrus interval (Figure 2). Thus, sows which return early after weaning should be inseminated relatively later in relationship to the beginning of estrus than late returning sows. Most studies have demonstrated that sows tend to ovulate about 2/3 into the estrus period. In order for spermatozoa to become “fertile” they must undergo capacitation in the female reproductive tract. Time required for capacitation is from 6 to 10 hours. Timing of insemination should be tailored for each farm situation, but a general recommendation for sows with once/day heat detection is to inseminate at 1st observed standing heat and again at 12 and 24 hours. However, from a practical standpoint, many farms inseminate at first standing heat and again at 24-hour intervals for as long as the sow remains in standing heat. One strategy is to delay insemination of sows, which return early after weaning for 12 or 24 hours, and inseminate sows, which return late after weaning immediately after detection.
Figure 3. Using weaning-to-estrus interval (WEI) as an aid in timing inseminations (Kemp and Soede, 1996).
ED = estrus duration (length), OEOI = onset of estrus-to-ovulation interal.
Management methods for the lean genotype sow are very important when trying to optimize sow herd productivity. The differences in how closely these management practices are followed are often the differences in observed reproductive performance. Management has to focus on closely maintaining body fat and weight during the reproductive cycle, maintaining a quality stress free environment and conscientiously following recommended breeding practices.
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